Endoscope apparatus using solid state image pickup device

ABSTRACT

An endoscope apparatus having an end section provided with an image forming optical system, a self-scanning type solid state image pickup device at which cyan and yellow color filters are positioned alternately to correspond to respective picture elements of the image pickup device, and a light guide. When green light is emitted from the light guide to an object, image signals corresponding to the green component of the object are picked up from all picture elements. When white light is emitted, cyan component image signals are picked up from the picture elements where the cyan filters are positioned, and yellow component signals from those where the yellow filters are positioned. Alternatively, when green light is emitted, green component signals are picked up from all picture elements and, when magenta light is emitted, blue component signals are picked up from the picture elements where the cyan filters are positioned and red component signals are picked up from those where the yellow filters are positioned. The image signals are then electrically processed to form a color image.

This application is a continuation of application Ser. No. 415,801,filed Sept. 8, 1982.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an endoscope apparatus used for observationand recording of the interior of a section unobservable from theexterior, and more particularly to an endoscope apparatus provided witha solid state image pickup device.

2. Description of the Prior Art

In general, endoscopes, also called fiber scopes, are used to observethe interiors of body cavities or equipment and record images of theinteriors. An end section of the fiber scope inserted into the interiorto be observed includes an image forming optical system for forming animage of an object, one end of an optical fiber bundle called an imageguide for transmitting the optical image created by the image formingoptical system to the other end of the image guide, and one end of anoptical fiber bundle called a light guide for illuminating the object.The optical image transmitted through the image guide is then enlargedby a loupe to facilitate observation, recorded on a photographic film ordisplayed by a CRT.

Recently, advances in semiconductor technology have led to the wide useof self-scanning type solid state image pickup devices, such as chargecoupled devices (CCDs), and television cameras using solid state imagepickup devices of this type have been put to practical use. The solidstate image pickup devices of this type have an advantage over the imagepickup tubes conventionally employed in television cameras, such asvidicons, in that they are smaller in size and lighter in weight. Underthe above circumstances, it has been proposed in Japanese UnexaminedPatent Publication Nos. 51(1976)-65962 and 49(1975)-114940 toincorporate a self-scanning type solid state image pickup devicedirectly in the above-described end section of an endoscope and convertthe image of an object formed by the image forming optical system intoan electric signal to display a television image on an image receiver(CRT display unit).

In general, to obtain a color television image on a CRT display unit,one of the image pickup systems described below will be employed. In thefirst and basic system, an image of an object formed by an image formingoptical system is colorseparated to red (R), green (G) and blue (B)color images, and three discrete solid state image pickup devicescorresponding to the three primary colors are used. In the secondsystem, only one solid state image pickup device is used, and red, greenand blue primary-color filters are arranged in a mosaic form forrespective picture elements of the solid state image pickup device toachieve multiplexing of the image pickup surface. In the third system,red, green and blue primary-color filters are rotated at a predeterminedspeed in front of a light source. The light source emits to theilluminating member of the endoscope, i.e. the above-mentioned opticalfiber bundle called a light guide, and the red, green and blueprimary-color components of the image are picked up in a planesequentialmanner from a single solid image pickup device. However, theseconventional systems present very real problems when used forendoscopes. Namely, the first system cannot be incorporated into a smalland thin end section of an endoscope, although it is the mostfundamental configuration and can provide good television images. If thefirst system is incorporated in the end section of an endoscope, the endsection becomes large and the application range of the endoscope islimited. The second system can be incorporated in a small end section ofan endoscope. However, in the second system, since the image pickupsurface of the solid state image pickup device is color-separated byred, green and blue primary-color filters arranged in a mosaic form, thenumber of the picture elements for the green component that determinesthe resolving power is reduced, resulting in a drop in the resolvingpower. Particularly, when the end section of the endoscope is madesmall, it is difficult to use a solid state image pickup device havingmany picture elements. In this case,therefore, a reduction in theresolving power presents a very real problem. In the third system, sincethe three primary color components of the image are sequentially pickedup by using a single solid state image pickup device in aplane-sequential mode, a problem concerning the timing of registrationof the three primary color image arises for an object moving at arelatively high speed, resulting in deterioration of the image quality.

SUMMARY OF THE INVENTION

The primary object of the present invention is to provide an imagepickup system suitable for an endoscope using a solid state image pickupdevice.

Another object of the present invention is to provide an endoscopeapparatus having a small endoscope end section.

The specific object of the present invention is to provide an endoscopeapparatus free from deterioration in resolving power and registrationerrors.

The present invention provides an endoscope apparatus using a solidstate image pickup device, the endoscope apparatus comprising:

(a) an image forming optical system for forming an image of an object,

(b) a self-scanning type solid state image pickup device for convertingthe image formed by said image forming optical system into an electricsignal, and

(c) an illuminating means for illuminating the object. These elementsare positioned in an end section of the endoscope for insertion into abody cavity, the interior of a machine or the like. The solid stateimage pickup device is provided with cyan and yellow color filtersalternately positioned to correspond to respective picture elements thatmake up the solid state image pickup device, whereby an image signalcorresponding to the green component of the object is picked up from allpicture elements of the solid state image pickup device when green lightis emitted from the illuminating means to the object, an image signalcorresponding to the cyan component of the object is picked up from thepicture elements of the solid state image pickup device where said cyancolor filters are positioned and an image signal corresponding to theyellow component of the object is picked up from the picture elements ofthe solid state image pickup device where said yellow color filters arepositioned when white light is emitted from the illuminating means tothe object, said image signals thereafter being electrically processedto form a color image. The color image signal obtained by electricallyprocessing the image signals by an image signal processor is thendisplayed as a color image on a display unit such as a CRT display unit.

The present invention also provides an endoscope apparatus having theconfiguration described above, wherein an image signal corresponding tothe green component of the object is picked up from all picture elementsof the solid state image pickup device when green light is emitted fromthe illuminating means to the object and, when magenta light is emittedfrom the illuminating means to the object, an image signal correspondingto the blue component of the object is picked up from the pictureelements of the solid state image pickup device where the cyan colorfilters are positioned and an image signal corresponding to the redcomponent of the object is picked up from the picture elements of thesolid state image pickup device where the yellow color filters arepositioned, the image signals thereafter being electrically processed toform a color image.

The endoscope apparatus in accordance with the present invention isprovided with only one solid state image pickup device, and yet achievesgreat improvements over the conventional systems with regard toresolving power and deterioration in image quality due to registrationerrors. Furthermore, the end section of the endoscope can be made smalland, therefore, the apparatus is very advantageous particularly inapplications where there is a limitation of the geometry and size of theend section.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing an embodiment of the endoscopeapparatus in accordance with the present invention,

FIG. 2 is a plan view showing a mosaic filter employed in the apparatusshown in FIG. 1,

FIG. 3 is a graph showing the spectral transmittances of the cyan andyellow filters contained in the mosaic filter shown in FIG. 2 and theintensity of the green component light picked up by the cyan and yellowfilters,

FIG. 4 is a schematic view showing another embodiment of the endoscopeapparatus in accordance with the present invention,

FIG. 5 is a graph showing the spectral distribution of source lightcontaining green light and magenta light and the spectral transmittancesof the cyan and yellow filters contained in the mosaic filter shown inFIG. 2,

FIG. 6 is a graph showing the distribution of the color component lightobtained by a combination of light source filters of FIG. 5,

FIG. 7 is a graph showing the spectral transmittance of the IR cutfilter employed in the apparatus shown in FIG. 4, and

FIG. 8 is a graph showing the distribution of the color component lightobtained by a combination of the light source filters of FIG. 5 and theIR cut filter exhibiting the spectral transmittance shown in FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will hereinbelow be described in further detailwith reference to the accompanying drawings.

FIG. 1 schematically shows the approximate configuration of anembodiment of the endoscope apparatus in accordance with the presentinvention. In FIG. 1, the endoscope apparatus comprises an endoscopebody 1, a light source unit 2, a synchronizing circuit 3, an imagesignal processing circuit 4 and an image display unit 5 such as a CRTdisplay. In an end section of the endoscope body 1 to be inserted intoan interior to be observed are incorporated at least an image formingoptical system 12 for forming an image of an object in the interior, aself-scanning type solid state image pickup device 13 such as a CCD, andan end portion 15 of a light guide 14 serving as an illuminating memberfor illuminating the object. At the solid state image pickup device 13,cyan (CY) and yellow (Y) color filters are positioned in a mosaic formas shown in FIG. 2 so as to correspond to respective picture elementsconstituting the solid state image pickup device 13. The end section ofthe endoscope body 1 shown in FIG. 1 is also provided with a windowglass 11, through which the image forming optical system 12 forms animage of the object on the image pickup surface of the solid state imagepickup device 13. The end portion 15 of the light guide 14 emits lightto the object throught the window glass 11. An electric image signal isobtained by the solid state image pickup device 13 and is sent throughta lead wire bundle 17 to the image signal processing circuit 4 and isthen displayed as an image on the display unit 5. The lead wire bundle17 includes lead wires for supplying clock signals used to drive thesolid state image pickup device 13, and the image signal processor 4contains a circuit for feeding the clock signals to drive the CCD.

The light source unit 2 is provided with flash lamps 25 and 26 which canbe alternately turned on and off at a high speed. A color temperaturecompensation filter 24 is positioned at the flash lamp 25, and a greenfilter 23 at the flash lamp 26. The green light and the white lightemitted from these light sources are sent through a semi-transparentmirror 22 and an IR cut filter 27 and condensed on an end face 16 of thelight guide 14 by a condenser lens 21. The flash lamps 25 and 26 areenergized by a power source (not shown), and are alternately turned onand off in synchronized relation to respective fields of an image by thesynchronizing circuit 3.

As described above, the cyan (CY) and yellow (Y) color filters shown inFIG. 2 are positioned at respective picture elements of the solid stateimage pickup device 13 shown in FIG. 1. Therefore, for example, when anodd image field (first field, third field, fifth field, ...) is exposedto light which exhibits the characteristics shown in FIG. 3 and which isgenerated by the flash lamp 26 and the green filter 23, the greencomponent signal (G) of the object is picked up from both pictureelements at which cyan filters are positioned and picture elements atwhich yellow filters are positioned, as shown in FIG. 3. Consequently,the green component signal of the object is picked up from all pictureelements of the solid state image pickup device 13. Then, when an evenimage field (second field, fourth field, sixth field, . . . ) is exposedto white light (W) (blue+green+red) which exhibits the characteristicsshown in FIG. 3 and which is generated by the flash lamp 25 and thecolor temperature compensation filter 24, the cyan component signal (CY)of the object is picked up from the picture elements at which the cyanfilters shown in FIG. 2 are positioned, and the yellow component signal(Y) of the object is picked up from the picture elements at which theyellow filters are positioned, as shown in FIG. 3. That is, the cyan andyellow component signals of the object are obtained from the even field.Thereafter, the green, cyan and yellow component signals are stored in amemory (buffer memory) contained in the signal processing circuit 4. Ablue component signal is generated by subtracting the green componentsignal from the cyan component signal, and a red component signal isgenerated by subtracting the green component signal from the yellowcomponent signal. In this way, television image signals are created bythe signal processing circuit 4. In this case, the resolving power forthe blue component signal and the red component signal of the object isonehalf the resolving power for the green component signal. However,because the resolving power for the color television images isdetermined by the resolving power for the green component signal, thesignal picking-up method described above does not adversely affect thecolor image resolving power. Furthermore, since signals of all colorcomponents of the objects are obtained from two fields, the timerequired to obtain all color component signals is twothirds the timerequired in the above-described conventional system for sequentiallypicking up the three-primary color image signals. Accordingly, theapparatus shown in FIG. 1 eliminates the problem concerning the timingof registration of three-primary color images, which arises in the thirdconventional system described above.

In the embodiment described above, the flash lamps that are turned onand off in synchronized relation to the fields are used as the lightsources. However, it is also possible to use light sources in whichgreen and magenta filters are rotated in synchronized relation to thefields. Furthermore, the mosaic filter comprising the cyan and yellowfilters positioned in one-to-one relation to the respective pictureelements of the solid state image pickup device may be replaced by astripe filter provided with stripes extending vertically with respect toFIG. 2.

FIG. 4 shows another embodiment of the endoscope apparatus in accordancewith the present invention. In FIG. 4, similar elements are numberedwith the same reference numerals as those in FIG. 1. The endoscopeapparatus shown in FIG. 4 has the same configuration as that shown inFIG. 1, except that a magenta filter 24' is positioned at the flash lamp25 instead of the color temperature compensation filter 24, and adichroic mirror 22' capable of reflecting green light and transmittingmagenta light is employed instead of the semitransparent mirror 22.

In FIG. 2, the cyan (CY) and yellow (Y) color filters shown in FIG. 2are positioned at respective picture elements of the solid state imagepickup device 13 as described above with reference to FIG. 1. Therefore,for example, when an odd image field (first field, third field, fifthfield, . . . ) is exposed to green light which exhibits thecharacteristics shown in FIG. 5 and which is generated by the flash lamp26 and the green filter 23, the green component signal (G) of the objectas shown in FIG. 6 is picked up from both picture elements at which cyanfilters are positioned and picture elements at which yellow filters arepositioned, as shown in FIG. 5. Consequently, the green component signalof the object is picked up from all picture elements of the solid stateimage pickup device 13. Then, when an even image field (second field,fourth field, sixth field, . . . ) is exposed to magenta light (M) whichexhibits the characteristics shown in FIG. 5 and which is generated bythe flash lamp 25 and the magenta filter 24', the blue component signal(B) of the object is picked up from the picture elements at which thecyan filters shown in FIG. 2 are positioned, and the red componentsignal (R) of the object is taken up from the picture elements at whichthe yellow filters are positioned, as shown in FIG. 6. That is, the blueand red component signals of the object are obtained from the evenfield. In this case, the resolving power for the blue component signaland the red component signal of the object is one-half the resolvingpower for the green component signal. However, the signal pick-up methodconducted in the apparatus shown in FIG. 4 does not adversely affect theresolving power for the color television images as already describedwith reference to FIG. 1. Furthermore, the apparatus shown in FIG. 4does not present the problem with regard to registration ofthree-primary color images because signals of all color components ofthe object are obtained from two fields and the time required to obtainall color component signals is two-thirds the time required in the thirdconventional system described above.

As shown in FIG. 4, the IR cut filter 27 is positioned in the lightsource unit 2. The IR cut filter 27 may exhibit the spectraltransmittance characteristics shown in FIG. 7. In this case, thespectral characteristics shown in FIG. 8 can be obtained by thecombination of light source filters 23 and 24' exhibiting thecharacteristics shown in FIG. 5 and the IR cut filter 27 exhibiting thecharacteristics shown in FIG. 7. Accordingly, the apparatus shown inFIG. 4 can achieve excellent color reproduction.

Furthermore, the image signal processing circuit 4 may process the imagesignals in various ways. For example, the green image signals that areobtained from the odd fields, and the blue and red image signals thatare obtained from the even fields may be alternately displayed forrespective fields on a color television monitor. Alternatively, theseimage signals may be stored in a memory and called to respective fieldsof the color television monitor to process the image signals assimultaneous color image signals.

What is claimed is:
 1. An improved endoscope comprising:means for emitting alternately colored beams of light onto a subject, a first one of said beams comprising a first color of light, and a second one of said beams comprising either a second color of light or white light; lens means for collecting said alternating beams of light, having been reflected from said subject; a self-scanning one-plate solid state image forming device, comprising a number of individual elements disposed with respect to said lens such that said light collected by said lens falls thereon and is detected thereby; means coupled to said image forming device for developing resolution and color signals; and filter means interposed betwen said lens means and said self-scanning solid state image forming device, said filter comprising filter elements of plural colors, each of which elements are substantially transparent to said first color of light but which selectively filter said second color or white light, such that a resolution signal is developed with respect to said first color and a color signal is developed with respect to said second or white light.
 2. The improved endoscope of claim 1, wherein said first color of light is green.
 3. The improved endoscope of claim 1, wherein said means for developing said resolution color signals comprises an image signal processing circuit connected to said self-scanning solid state image forming device.
 4. The improved endoscope of claim 3 further comprising a display unit connected to said image signal processing circuit.
 5. The improved endoscope of claim 1 wherein said means for emitting alternately colored beams of light onto a subject comprises a light source unit comprising two flash lamps, a color temperature compensation filter positioned in front of one flash lamp, a filter for passing only said first color of light position in front of the other flash lamp, and a semi-transparent mirror for directing light from said color temperature compensation filter and light from said filter for passing only said first color of light towards said illuminating means.
 6. The improved endoscope of claim 5 wherein said light source unit further comprises an infrared cut filter positioned to receive light from said semi-transparent mirror.
 7. The improved endoscope in claim 5 further comprising a synchronizing circuit connected to said flash lamps for alternately turning said flash lamps on and off.
 8. The improved endoscope of claim 1 wherein said second color of light is magenta light.
 9. An improved endoscope comprising:means for emitting alternately colored beams of light onto a subject, a first one of said beams comprising a primary color of light and a second one of said beams comprising either a secondary color of light or white light; lens means for collecting said alternating beams of light, having been reflected from said subject; a self-scanning one-plate solid state image forming device, comprising a number of individual elements disposed with respect to said lens such that said light collected by said lens falls thereon and is detected thereby, said self-scanning solid state image forming device comprising means for outputting signals responsive to the intensity of light falling on the individual elements thereof; filter means interposed between said subject and said self-scanning solid state image forming device, said filter means consisting essentially of filter elements of two types, both of said types of elements being substantially transparent to said primary color of light but selectively filtering said secondary color of light or white light; and means for developing resolution signals from the signals emitted by said self-scanning image forming device with respect to said primary color and for developing color signals from the signals emitted by said solid state image forming device with respect to light of said secondary or white color, as filtered by said filter elements.
 10. The improved endoscope of claim 9 further comprising an image signal processing circuit connected to said means for developing resolution and color signals, and a display unit connected to said image signal processing circuit.
 11. The improved endoscope of claim 9 wherein said means for emitting alternately colored beams of light comprises a light source comprising two flash lamps, a color temperature compensation filter positioned in front of said flash lamps and a filter for filtering all but said primary color of light positioned in front of the other of said flash lamps, and a semi-transparent mirror for directing light from said filters towards said subject.
 12. The improved endoscope of claim 11 wherein said light source further comprises an infrared cut filter positioned to receive light from said semi-transparent mirror.
 13. The improved endoscope as defined as claim 11 further comprising a synchronizing circuit connected to said flash lamps for alternately turning said flash lamps on and off. 